The usual cause of duplicate emails is that something along the chain through which the message passes is failing to acknowledge the receipt of messages.
As an email goes from one server to another the receiving server is meant to send back a message which effectively says "Thanks. I've got that". If the message gets through but the acknowledgement isn't sent back (or is sent but fails to arrive) the sending server assumes that the message has not got to where it should be and sends it again. If it then fails to get an acknowledgement it sends the message repeatedly until either it finally gets an acknowledgement or it reaches the pre-set limit on its attempts. In some cases that limit is very high, meaning that a failure in the acknowledgement system can result in someone receiving hundreds of copies of the same email. (The highest number of copies of a single email that I've ever had was 2000).
If you're getting multiple copies of emails on your iPad, but not elsewhere, it suggests that it's only at the very last stage of an email's journey that the problem is occurring. i.e. the iPad's email app is failing to get acknowledgements through. That could simply be because of a poor connection to the internet but it might be something related to the app itself.
Try deleting your account in the app and then creating it again. (That seems to fix many email problems - often for no apparent reason!). Alternatively try a different email app. Assuming that you're currently trying to use the default app on your iPad, the obvious alternative is this one:
https://itunes.apple.com/gb/app/yahoo-mail/id577586159?mt=8